KDE. Yes, it switches back to what is probably the default setting. You asked two questions in one. No to both not for a long time. I haven't done a fresh install on this box for a while just keep updating and haven't changed user accounts for a while either. The only reason I changed user accounts back when I did was to fix a problem in the old user account settings.
Twice tonight the font type and size changed. The selection color probably did too but I only saw that after I was opening a file in Vim.